The larger question for me Dave, is how come that knowledge became world wide?
Disregard the theories that man invented fire, or that it was a naturally occurring phenomena via lightning, and focus on just how wide the usage was. Just how, in a world where travel and communication was limited, did
all the races learn to cook by fire? How was that discovery made universal when mere mortals couldn't communicate as they can now?
There's something to be said for Von Daniken's theories, despite him coming in for a lot of criticism. Whether you believe or not, he's a bloody good read when the wind's blowing
http://en.wikipedia.org/wiki/Erich_von_D%C3%A4niken
kev